An emulsified fuel is an emulsion composed of water and a combustible liquid, either oil or fuel. Emulsions are a specie of dispersions comprising a continuous and a dispersed phase, where both phases (oil and water) are immiscible liquids.
Water continuous (oil-in-water) emulsified fuels are sometimes referred to as high internal phase emulsions (hipe) because the continuous phase is around 30% of the composition of the fuel. Oil continuous (water-in-oil) emulsified fuels are exemplified by diesel (or biodiesel blended fuels) and water emulsions.
Water-in-oil emulsions have recently been engineered to control the stability and quality of the emulsion to make it advantageous for industrial and power-generating uses. (See, FSI Energy “Discussion of Water-in-Oil Emulsion Combustion” available at http://fsienergy.com/H20INOIL.htm, the entire contents of which are hereby incorporated by this reference). These water-in-oil emulsions are said to yield reduced carbon particulates, lower opacity, and lower nitrogen oxide levels.
In the combustion of a water-in-oil emulsion, the primary spray fuel droplets are further divided as a result of the explosive vaporization caused by rapid heating of the water dispersed within the individual fuel droplets. The internal water droplets undergo spontaneous nucleation of steam bubbles, causing a violent conversion of the water droplet to steam. The vaporization, in turn, produces a rapid expansion of the surrounding oil droplets, fragmenting the oil into a vast number of smaller fuel droplets in a process known as secondary atomization.
Presently known techniques for manufacturing water-in-oil emulsions involve the simultaneous mechanical agitation of the water and oil in the presence of surface active agents, referred to herein as emulsifiers or surfactants, to enhance the stability of the emulsion. (See Mohammed Yahaya Khan, Z. A. Abdul Karim, Ftwi Yohaness Hagos, A. Rashid A. Aziz, and Isa M. Tan “Current Trends in Water-in-Diesel Emulsion as a Fuel” available at http://www.hindawi.com/journals/tswj/2014/527472/, the entire contents of which are hereby incorporated by this reference).
Surfactants may be described as comprising a polar (hydrophilic) head and a nonpolar (hydrophobic) tail, and serve to weaken the surface tension, or intrinsic adhesion, of the host medium. When dissolved in an oil-water mixture, the polar groups orient toward the water and the nonpolar groups orient toward the oil to lower the interfacial tension between the oil and water phases. For this purpose, surfactants may be characterized by a hydrophilic-lipophilic balance or HLB (water liking-oil liking) score. In particular, Griffin's method generally expresses the HLB value for non-ionic surfactants asHLB=20*MH/M where MH is the molecular mass of the hydrophilic portion of the molecule, and M is the molecular mass of the entire molecule. (See Griffin, William C. (1949), “Classification of Surface-Active Agents by ‘HLB’”, Journal of the Society of Cosmetic Chemists; and Griffin, William C. (1954), “Calculation of HLB Values of Non-Ionic Surfactants”, Journal of the Society of Cosmetic Chemists, the entire contents of which are hereby incorporated by this reference). Lower HLB values are more lipophilic and tend to promote water-in-oil-emulsions, while higher HLB values are more hydrophilic and tend to promote oil-in-water emulsions. Other methods may also be used to determine HLB values; See Davies J T (1957), “A quantitative kinetic theory of emulsion type, I. Physical chemistry of the emulsifying agent”, Gas/Liquid and Liquid/Liquid Interface (Proceedings of the International Congress of Surface Activity), the entire contents of which are hereby incorporated by this reference).
Surfactants used in water-in-oil emulsions are generally selected to ensure that the water remains dispersed within the continuous oil phase, and thus tend to have lower HLB values, for example in the range of up to about 6. In contrast, surfactants used in oil-in-water emulsions are selected to ensure that the oil remains dispersed within the continuous water phase, and thus tend to have higher HLB values, for example in the range of 10 and above.
Presently known emulsified fuels are limited, however, in that they tend to have a limited shelf life; that is, they tend to separate after a few hours or days. Systems and methods are thus needed which overcome the limitations of the prior art.
Various features and characteristics will also become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background section.